INTERPRETATION OF HOT AND DENSE ABSORPTION-SPECTRA OF A NEAR-LOCAL-THERMODYNAMIC-EQUILIBRIUM PLASMA BY THE SUPER-TRANSITION-ARRAY METHOD

The super-transition-array model is shown to be a very convenient tool for the interpretation of near-local-thermodynamic-equilibrium hot an d dense plasmas. Specifically, we interpret here the absorption spectr a of the CH-Ni-CH foil experiment performed at Lawrence Livermore Nati onal Laboratory using the backlighter technique. In this experiment a laminar foil composed of 200-Angstrom Ni with 1000-Angstrom CH on both sides was radiatively heated by the x-ray continuum from a nearby gol d plasma and was backlit by the x-ray continuum from a distant gold pl asma that could be time delayed with respect to the heating pulse. Thi s setup was designed to achieve a uniform density and heating of the N i middle layer. It is found that the Ni absorption features depend ver y weakly on the density of the foil but are quite sensitive to the foi l temperature. Remarkably good agreement between the theory and the ex periment is obtained for the Ni 2p-3d spectrum. The detailed features indicate that the plasma temperature-is confined to a narrow range bet ween 14 and 18 eV, demonstrating that the foil design, aiming to creat e a homogeneous Ni plasma, was successful. These results represent an alternative temperature diagnostic for high-Z plasma.